1. Field of the Invention
This invention relates generally to pressure measurement devices. More specifically, it relates to devices which measure the difference in pressure between two regions in demanding applications such as in the cooling loops of nuclear reactors.
2. Related Art
There are many industrial applications where pressure, or differences in pressure, need to be measured. For example, in pipelines containing an internal narrowing aperture, or orifice plate, the pressure on the upstream side of the orifice plate will be greater than the pressure on the downstream side of the orifice plate. The difference in pressure between these two regions is directly related to the speed of fluid traveling in the pipeline. Therefore, in applications where the rate of fluid flow needs to be accurately and reliably measured, the pressure-sensing device which indirectly indicates this fluid velocity needs to be commensurately accurate and reliable.
In particularly demanding applications, the pressure measurement device must be able to withstand very high pressures. These pressures may also be applied very suddenly, as when a wave front hits the upstream side of the pressure detector. Of course, it is important that the pressure detector not sustain any damage during the occurrence of these pressures. But also, it is imperative that the sensitivity, accuracy, and continued functioning of the pressure detector over a wide pressure range is not compromised by these occurrences.
Certain known high-pressure protection arrangements comprise valves which close completely at a predetermined pressure threshold to prevent any further pressure increases from damaging the device's pressure-sensitive elements. One particular known system has the valves disposed internally, to isolate incompressible fluid within a pressure-sensitive element so that it is not compressed further by any additional pressure increases. Whereas this protective valve arrangement does prevent damage to the pressure-sensitive elements, the valves sometimes may not reopen when the excessive pressure is removed, resulting in a "lockup" of the device and a subsequent total loss of pressure measurement capability.
Also, it is important in many demanding applications, such as in the cooling loops of nuclear reactors, that the sensitivity and accuracy be maintained over a wide temperature range. Known systems whose pressure measurements depend on displacement of an internal fluid often have the characteristic that the pressure measurement "wanders" as the temperature rises due to thermal expansion of the internal fluid, even though the actual pressure remains stable.
Known pressure measurement devices which depend on incompressibility of the fluid contained within them often suffer from the effects of unwanted gaseous bubbles contained within the fluid. The pressure of these bubbles compromises the effective incompressibility of the fluid, thereby decreasing accuracy and reliability of pressure measurement.
Finally, as in any commercial setting, many known systems do not achieve their objectives economically. Their manufacture, assembly, installation, operation, and/or maintenance may be too expensive to be cost-justified.